So even though I'm an avid fan of the Mac operating system, I try to use open source tools as much as possible (since part of my job is advocating that NGO's around the world use open source). I've successfully weened myself off of Microsoft Office and now solely use Open Office (which I really do like by the way).
I've tried to switch my web-browser several times. Firefox is probably the best damn web-browser on the planet and it seems ridiculous that I use the Mac's Safari browser over it all the time, especially since Safari often runs into problems with certain scripts on web-pages. The issue though comes down to performance. Firefox running on my little Chicklet (my 12" power mac G4) brings the whole system to its knees. I can't listen to iTunes at the same time without massive pauses - its extremely irritating! Also the rainbow pinwheel will appear constantly and pause me in the midst of whatever typing I'm doing. So I last maybe 2 hours in Firefox and then switch back to Safari.